Historically, electricity has been metered by using electromechanical meters and more recently solid-state meters. In those instances where it is necessary to meter electricity at a voltage higher than 120V, instrument transformers are used to step down the voltage to the nominal input voltage of the meter, usually 120V. Because these instrument transformers are required to provide enough energy to drive the mechanism of the meter while still maintaining a precise voltage ratio, they are quite large, heavy, and expensive.
Traditionally, a potential transformer (PT) can be used for voltage sensing, but PTs are very large and heavy. To maintain accuracy and to negate ratio errors due to loading, PTs are typically oversized so that they reproduce voltage faithfully across the loading range. For example, for a 1 volt-ampere (VA) loading, a PT rated at 25 VA is typically used and can weigh several pounds. Galvanic isolation provided by transformers is important to maintain in metering applications to isolate circuits coupled to the secondary side from circuits coupled to the primary side, where high levels of voltage are present. Metering voltage by providing only a voltage divider circuit directly from the line would not provide the requisite galvanic isolation.
What is needed, therefore, is a compact voltage sensing solution. The present disclosure is directed to addressing these and other needs.